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Optimal hearing may be as fleeting as youth itself. It is too often sacrificed on the altar of social pressures and modern lifestyle–from over-amplified clubs, concerts, and sporting events to the ubiquitous use of earbuds pulsing the latest hits directly into tender ears. While exposure to loud recreational noises has long been recognized to cause tinnitus and hearing impairments over time, new research is escalating emphasis on the risky listening habits posing serious health threats to even more young people.

“The prevalence of tinnitus has been increasing worldwide, while the age of affected subjects has been decreasing,” said Tanit Ganz Sanchez, MD, PhD, associate professor at the University of São Paulo Medical School, director of Ganz Sanchez Institute, and president of the Association for Interdisciplinary Research and Divulgation of Tinnitus in São Paulo, Brazil. Today's teens with tinnitus will be the adults of tomorrow who will present more hearing problems and labor incapacity.

In fact, the World Health Organization (WHO) already raised a red flag, stating that “some 1.1 billion teenagers and young adults are at risk of hearing loss due to the unsafe use of personal audio devices, including smartphones, and exposure to damaging levels of sound.” Quantifying the global breadth of hearing loss, WHO reported that 360 million people have moderate to profound hearing loss, but “it is estimated that half of all cases of hearing loss are avoidable.”

ADOLESCENTS AT RISK

Mounting evidence shows that damage wrought by risky listening is occurring at an earlier age than previously thought, with many teens already struggling with hearing loss, tinnitus, and hyperacusis. In earlier research on tinnitus prevalence in children, Sanchez and colleagues surprisingly found a significant incidence, with 37 percent of the children presenting with the condition (Coelho. Prog Brain Res 2007;166:179 http://bit.ly/2bDHrO3).

“These alarming data prompted us to investigate this issue in adolescents, considering the numerous situations of noisy leisure enjoyed by this age group,” Sanchez explained. “We took into consideration that noise exposure is cumulative over a lifetime and that while present scientific concern is more directed to professional noise than to the leisure habits, modern life, especially in big cities, provides the beginning of exposure to recreational noise in phases ever earlier in life, including childhood.”

“What was unique about the study was it included a full audiological evaluation on all 170 teens,” noted co-author Larry E. Roberts, PhD, of McMaster University (Sanchez. Scientific Reports 2016;6:27109 http://bit.ly/2apjbfS). “We measured their audiograms, testing sound thresholds for hearing up to 16 kilohertz, the limit for functional hearing–most researchers only measure half of that. We also measured otoacoustic emissions emitted by the healthy ear.”

Sanchez said they found the prevalence of tinnitus was higher in teens than in the general population: 54.7 percent (identified through a questionnaire) and 28.8 percent (through measurement in an acoustic chamber).

“There was one surprise after another,” Sanchez explained. “I thought that we would find about 30-40 percent of teenagers with tinnitus, similar to our study with children, but we found much more. I also thought those with tinnitus would have alterations in their audiometry and/or otoacoustic emissions, but they didn´t, so none of the exams could discriminate between those who have or do not have tinnitus,” she said. “Regarding the measurement in the acoustic chamber–which was the innovation in this prevalence study–I confess that I had no previous idea about the result. So, I was quite astonished.”

A CHANGE IN SOUND TOLERANCE

Although the hearing thresholds and otoacoustic emissions were the same as the teens who had never had tinnitus, the researchers did find one important difference: the level of sound that the teens found to be uncomfortable. Teens with a history of tinnitus were much more sensitive to sounds than their unaffected peers.

Roberts explained that when auditory nerve cells are damaged, brain cells increase their sensitivity to their remaining inputs, which makes ordinary sounds seem louder. “We know that increased sensitivity to loud sounds probably is an indication that there is damage to the auditory nerve fibers that convey sound information from the ear's hearing receptors (called hair cells) to the brain. Once the synapses that connect the nerve fibers to the hair cells are damaged, they do not recover. Over a period of years the affected auditory nerve fibers will die. That is hearing loss that will not show up in an audiogram when we are young but will likely be evident years later.”

Tinnitus, then, may represent the first indication of injury to auditory nerve fibers, which has been shown to be progressive over the lifetime in animal studies. “If this also happens to adolescents, this and the next generation will face a big problem,” warned Sanchez. “Genetics may suggest the ability to live up to 100 years of age, but leisure habits suggest the existence of hearing loss for many of those years.”

EARPLUGS STILL WORK

It may be naive to think that arming kids with earplugs can hold down the hearing loss offensive, particularly given the multiplicity of technology that trades off protective plugs for offending headphones and earbuds. However, when pressed into service, earplugs remain an inexpensive and effective protection, as seen in a single-blind clinical trial conducted at an outdoor music festival in Amsterdam (Ramakers. JAMA Otolaryngol Head Neck Surg 2016;142[6]:551 http://bit.ly/2bE5Kvc). Normal-hearing adult volunteers were recruited via social media. Of the 51 participants, 25 were randomized to the earplug group and 26 to the unprotected group. The groups had similar gender, age, and baseline representation. Results showed that newly induced tinnitus following sound exposure occurred in three of the 25 participants (12%) in the earplug group, compared with 10 of 25 (40%) in the unprotected group. The researchers concluded that earplug use “is effective in preventing temporary hearing loss after loud music exposure. The present randomized clinical trial adds proof to the scarce evidence and knowledge on this topic, which is a growing global problem.”

HIDDEN HEARING LOSS

To complicate things a bit more, noise-induced hearing loss may be concealed in a “black hole” on the audiogram, remaining stealth and undetectable on standard tests. In a previous article in The Hearing Journal, Sharon G. Kujawa, PhD, director of the Department of Audiology at Massachusetts Eye and Ear Infirmary and principal investigator in the Eaton–Peabody Laboratories, discussed a form of hidden hearing loss related to age and noise. She explained that work on these fields recently revealed an “insidious process that progressively interrupts communication between sensory hair cells and auditory neurons, leading ultimately to death of the neurons themselves. These neurodegenerative changes are likely very common, occurring even in ears with normal threshold sensitivity and a full complement of hair cells; thus, they present challenges to our traditional approaches to diagnosis and management.”

TECHNOLOGY LEAPS AHEAD

Beyond earplugs and sound blocking headphones, a new technology is emerging for the purpose of music appreciation, but with a potential to impact hearing technology overall. The brainchild of an Australian startup team, “Nura” headphones detect and analyze otoacoustic emissions in the wearer's ears, then equalize the sounds to deliver just the right mix of bass and treble, allowing the wearer to enjoy thumping bass without it overshadowing delicate vocals. In short, every wearer gets music delivery customized to their own hearing.

“The basic otoacoustic emission [OAE] technology underlying Nura has been around for decades,”said Luke Campbell, MBBS, BMedSc (Hons), one of Nura's creators. “However, there have been advances in the last few years regarding the separation and significance of the different sources of OAE responses.”

He explained that Nura headphones utilize both in-ear and over-ear components. A sensitive microphone is placed in the ear canal by way of an earbud-like structure inside the headphone. The microphone reads emissions coming from the ear and determines which frequencies are heard well and which are not. This information is registered in the headphone component that then modifies and customizes the sounds flowing into the ear.

“The magic is really in understanding the strengths and limitations in the interpretation of OAE measurements and working out the best way to use that data to enhance music for the listener.”

Campbell also assuredly explained why Nura headphones are less likely to negatively impact hearing than standard headphones or earbuds. “The new hybrid in-ear/over-ear design actually makes Nura safer. The over-ear part plays powerful deep base you can feel (on your skin) while the occluding in-ear section blocks most of that sound from moving your tympanic membrane. This means users don't have to increase the volume to dangerous levels to feel the beat. The double passive isolation also means the user does not need to increase the volume to compete with ambient noise.”

While providing an optimal musical experience of music has always been Nura's primary focus, Campbell noted another feature that may aid risky listening habits. “Users will be able to easily visually track changes in their hearing over time on the Nura app. As a medical professional, I would hope that users who objectively see their hearing declining will be prompted to seek audiological/otological attention earlier than would otherwise be the case.” Campbell believes this constant awareness of hearing changes may prompt users to avail themselves of occupational noise protection measures and recreational listeners to turn the volume down by one or two notches.

Whether Nura will ever be adopted by the medical hearing community for any purpose has yet to be determined. But the utility of portable, wearable, and recreational hearing screeners is undeniable. “One of the huge potentials lies in what we could learn from having tens of thousands of OAE capable headphones spread all over the world collecting data (only when users consent) about hearing in general, OAEs, and changes in hearing over time,” remarked Campbell.

He believes headphones of the future are going to become smarter – “… noise cancelling was just the start.” And while Nura has personalized sound and can identify the user, other products have become completely wireless and have added heart-rate and oxygen monitoring and selective filtering.

“What this means for hearing professionals is that there are going to be a lot more products able to objectively or subjectively measure and track hearing and a lot more devices blurring the lines between headphones/earphones, personal amplification devices, and hearing aids,” Campbell declared. “I would expect to see direct noise dosimetry starting to be added as a feature in smart headphones, and it may end up being the case that smart consumer headphones with noise dosimetry and the ability to test a user's hearing over time (months to years) will become the source of the dataset that eventually informs noise-induced hearing loss guidelines.”

Considering the risky listening habits of younger populations, Roberts also approved of measuring noise exposure. “Tracking dosimetry is a good idea whose time may soon come,” he said. “But for the present, while devices such as Nura offer benefits for pleasurable listening, the level of protection for hidden hearing loss needs to be tested.”